Corn stover is expected to supply much of the cellulosic biomass required to meet the 61 billion liters per year target under the US Energy Independence and Security Act. The Act also requires that cellulosic biofuels achieve a greenhouse gas (GHG) reduction of 60% compared to gasoline. If corn stover is harvested for biofuels, it can no longer help replenish soil organic matter, and net soil carbon emissions increase. So meeting the GHG reduction target is a concern. We studied the effect of stover removal on overall GHG emissions of corn stover ethanol systems in the 12-state Corn Belt region. Even at a stover removal rate of 66%, no more than 20 billion liters can be annually produced while simultaneously satisfying the 60% GHG reduction. Moreover, no GHG reduction relative to gasoline occurs in short time periods. The GHG benefits of corn stover ethanol only appear after longer time periods.
Increased clustering and consolidation of livestock production systems has been linked to adverse impacts on water quality. This study presents a methodology to optimize manure management within a hydrologic region to minimize agricultural phosphorus (P) loss associated with winter manure application. Spatial and non-spatial data representing livestock, crop, soil, terrain and hydrography were compiled to determine manure P production rates, crop P uptake, existing manure storage capabilities, and transportation distances. Field slope, hydrologic soil group (HSG), and proximity to waterbodies were used to classify crop fields according to their runoff risk for winter-applied manure. We use these data to construct a comprehensive optimization model that identifies optimal location, size, and transportation strategy to achieve environmental and economic goals. The environmental goal was the minimization of daily hauling of manure to environmentally sensitive crop fields, i.e., those classified as high P-loss fields, whereas the economic goal was the minimization of the transportation costs across the entire study area. A case study encompassing two contiguous 10-digit hydrologic unit subwatersheds (HUC-10) in South Central Wisconsin, USA was developed to demonstrate the proposed methodology. Additionally, scenarios representing different management decisions (storage facility maximum volume, and project capital) and production conditions (increased milk production and 20-year future projection) were analyzed to determine their impact on optimal decisions.
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